SECAM Sega Mega Drive Adapter Compatibility Mod
SECAM variants of the model 1 Sega Mega Drive (mostly from France and Switzerland, models 1600-09 and 1601-09) are wired slightly differently, and don't work with the standard HD Retrovision model 1 to model 2 adapter. A special adapter for these variants was made, but it was produced in extremely limited quantities, so it's almost impossible to keep it in stock.
Luckily, there is a very simple mod that you can perform on one of these SECAM consoles to make it compatible with the standard HD Retrovision Genesis 1 adapter. You simply need to bridge two pins on the multi-out connector, which can be done with even extremely limited soldering experience.